The present invention relates to breathable absorbent articles such as sanitary napkins, pantyliners, and incontinence pads which are adhered to an undergarment during use. More particularly the present invention relates to articles which are air permeable or breathable and which have a flexibility in a longitudinal direction which provides improved comfort to the wearer of the article.
Disposable absorbent articles such as baby diapers, adult incontinence articles, sanitary napkins and panty liners are well known in the art. These articles have a wearer facing side through which they typically absorb liquids discharged by the wearer. The liquid is stored in an absorbent structure. Liquid leakage from the article through the surface opposite the wearer facing side is usually prevented by incorporating a liquid impermeable backsheet on that side.
It is also well established in the art that a backsheet allowing gaseous fluid (air) communication with the environment, usually referred to as breathability, is highly desirable. Breathability improves with the amount of air permeating through a backsheet. This amount is proportional to the open area (the sum of the area of all apertures) in the backsheet. Obviously too many and particularly too large apertures in the backsheet lead to compromising the liquid leakage prevention, which is the primary function of a backsheet.
Many suggestions how to provide breathable backsheets have been recorded in the art. Numeral attempts of combining the mutual contradicting features of gas permeability and liquid impermeability have been documented in patents and patent applications. However the lack of commercially available breathable disposable absorbent articles indicates that the technology so far suggested has not provided an all around satisfactory result for the desired technical requirements at commercially acceptable conditions. More often than not satisfaction of one desired feature went to such an extreme that the respective other feature was not properly satisfied any longer.
For example sanitary napkins with very high breathability at the cost of frequent liquid leakage (leading to soiling of the undergarments of a wearer) cannot be considered satisfactory. On the other hand satisfying the liquid leakage problem properly usually resulted in almost impermeable, that is non-breathable, backsheets.
Combinations of breathable and liquid permeable sheets in order to provide a certain liquid impermeability while satisfying the desire for breathable backsheets have already been suggested for example in U.S. Pat. No. 3,881,489. In this disclosure a breathable backsheet is provided by confining an outer layer of formed film material having surface aberrations with apertures therein and an inner layer of a paper tissue having a high void volume and having been made hydrophobic by impregnating it with a paraffin wax. This document does not disclose the desire for using a directional liquid transport type polymeric film structure with a hydrophobic fibrous fabric layer made of polymeric material.
Other prior art attempts to provide breathable backsheet assemblies comprising more than one layer are e.g. documented in U.S. Pat. No. 4,341,216, EP-A-109 126 or EP-A-203 821. Neither of these disclosures provides constructions of breathable backsheets similar to the present invention.
Single layer breathable backsheets are known for example from GB-A-2184391, GB-A-2184390, GB-A-2184389, U.S. Pat. Nos. 4,591,523, 4,839,216 or EP 156471. None of the mentioned disclosures attempts however to address the comfort problems associated with stiff or not sufficiently flexible absorbent articles.
Another solution to the problem of conflict between leakage and breathability is of course to provide so much absorbent material that leakage is prevented by liquid retention rather than impermeability of the backsheet. This leads to early designs of catamenial articles having a very thick absorbent core with a fully permeable non-woven or gauze wrapping. However these articles are not used any longer due to being extremely uncomfortable. Also they are too costly due the high material consumption required in order to provide the end user with peace of mind regarding the leakage performance of these articles.
Also this solution, as did other alternatives which increased material consumption, causes the absorbent article to become less flexible. Flexibility in particular the ability to bend and twist easily in longitudinal and preferably in all directions has however become of key importance especially for everyday usage absorbent articles such as panty liners, sanitary napkins and incontinence pads.
Such sanitary napkins, pantyliners, and incontinence pads are typically worn in the crotch region of an undergarment and attached to the undergarment by a so called panty-fastening-adhesive. In order to be comfortable to the wearer these articles need to be flexible. It is believed that the more flexible an absorbent article is the less will it be noticeable to the wearer. Hence this provides comfort by more closely resembling the situation when no such absorbent article is worn.
Flexibility can easily be achieved by reducing the amount of material in an absorbent article or replacing stiff or inflexible components by more flexible ones. However it has long been recognised that extreme flexibility can reduce the absorbent performance of these articles, for example by an insufficient amount of absorbent material or by bunching or densifying of the absorbent material during use. Also a too flexible article may be difficult to handle for the wearer when attaching it to the undergarment.
The problem of too much flexibility in an article due to a low amount of inflexible material has been addressed for example in U.S. Pat. No. 4,217,901 where particularly the stiffness of an absorbent article is increased in order to provide satisfactory performance. This prior art reference accepts the comfort implications caused by its stiffness requirement. Also breathability is not even considered in this document. Therefore flexibility and leakage prevention (as well as breathability and leakage prevention) are mutually apposite characteristics of absorbent articles. Hence flexibility and breathability combined are working in synergy against leakage prevention while all three features are highly desirable.
It now has been found that the comfort of breathable absorbent articles can be drastically improved when providing a high flexibility in longitudinal direction in combination with a particular panty-fastening-adhesive configuration so as to maintain the breathable article flat relative to the undergarment of the wearer. The flexibility then becomes limited only by material requirements (e.g. to provide sufficient absorbent performance) and by handling requirements of the absorbent article.
It is therefore an objective of the present invention to provide sanitary napkins with an improved flexibility without the previously experienced drawbacks. In particular a high degree of flexibility and breathability in the absence of bunching problems without major handling difficulties is achieved by the selected ranges of design parameters of the articles according to the present invention.
It is another objective of the present invention to provide highly flexible absorbent articles in particular sanitary napkins or panty liners having a superior breathability of the backsheet while simultaneously retarding liquid leakage through the backsheet to such an extend that the user of such articles does not experience a recognisable difference between a liquid impermeable backsheet and the breathable backsheet according to the present invention.
These and other objectives of the present invention will be more readily apparent when considered in reference to the following description.
The present invention provides a breathable absorbent article such as a sanitary napkin, an incontinence pad and particularly a panty liner for use in an undergarment. The absorbent article has a breathable backsheet which comprises a garment facing surface. On the garment facing surface is an adhesive to adhere the article to the undergarment. The article may optionally comprise protective side-flaps which during use are folded around the side edges in the crotch region of the undergarment so as to improve soiling protection for the undergarment. The absorbent article also comprises the other typical components of such articles namely an absorbent core and a liquid pervious wearer facing surface which is preferably provided by a liquid pervious topsheet. The absorbent article comprises a breathable backsheet which usually provides the garment facing surface of the absorbent article. If topsheet and backsheet are present the absorbent core is enclosed by them on the wearer and on the garment side respectively.
The adhesive can be provided across the whole, part or several distinct parts of the garment facing surface. The adhesive is provided so as not to clog the full surface area. If it covers the whole garment facing surface it can be in a filamentary fashion which is random or in a defined design like spirals. The total area of all adhesive on the garment facing surface of the absorbent article defines the actual adhesive surface. In addition a theoretical adhesion surface is given by the periphery of an endless line which is the shortest encircling line of the adhesive without extending beyond the periphery of the garment facing surface itself.
The absorbent article according to the present invention has a surface ratio of theoretical adhesion surface to the garment facing surface in a range of 0.6 to 1, preferably 0.85 to 1 for articles without the protective side flaps and in a range of 0.5 to 1, preferably from 0.7 to 0.9 for articles with protective side flaps. In a preferred embodiment the theoretical adhesion surface is substantially coextensive to the actual surface covered by the adhesive.
In order to realise the benefits of the present invention the absorbent article as a whole needs to provide exceptional flexibility. The flexibility is measured by the modified ASTM method D1388 as described herein below in longitudinal direction. The expression xe2x80x9cflexibilityxe2x80x9d is also referred to as xe2x80x9cdrapabilityxe2x80x9d due to the particular method. It should be understood that stiffness is characteristic of the opposite behaviour of a material. The flexibility should be in the range of 1300 to 5000, preferably from 2000 to 3500, most preferably 2000 to 3000, mgxc3x97cm.
These flexibility values in combination with the surface ratio indicated above provide exceptional wearer comfort without soiling and/or absorbent performance problems due to bunching or densification of the absorbent material and still allows the wearer to attach the article to the undergarment without undue effort. According to the present invention flexibility is measured in longitudinal direction because this is the value more readily measurable and important. In principle the transverse flexibility also could be used, possibly at different values. Due to the small extension of articles in the transverse direction it is however usually not possible to properly measure flexibility in this direction.
The thickness of a preferred embodiment of the present invention especially for pantyliners is less than 3 mm and even more preferably in the range of 0.5 to 1.5 mm according to the thickness measurement method described herein below.
The combination of appropriate panty-fastening adhesive coverage and flexibility is particularly useful in the context of stretchable absorbent articles. Absorbent articles being stretchable in one direction and more so absorbent articles being stretchable in two (or all) directions are inherently flexible. Stretchability in itself already provides an improvement for comfort such that the absorbent articles combining stretchability with the present invention are particularly desirable.
Particularly useful are stretchable absorbent articles having the stretch characteristics described in U.S. application Ser. No. 08/192,240 filed Feb. 4, 1994 and indicated in the Table of FIG. 7 and the respective description of that application.
The second key aspect according to the present invention is the breathability of the backsheet of the absorbent articles. The articles according to the present invention have a breathable backsheet comprising an inner layer and an outer layer where the inner layer is closer to the absorbent core than the outer layer. The outer layer comprises a hydrophobic, gas permeable fibrous fabric layer composed of polymeric fibres such as polymeric non-wovens well known in the art of absorbent articles.
The inner layer comprises a hydrophobic gas-permeable (air-permeable) polymeric film such as a microporous film having micro-apertures or a macroscopically expanded, polymeric film having macro-apertures.
If the inner layer comprises a hydrophobic gas-permeable micro- or macro-apertured, polymeric film, it preferably has a directional liquid transport phenomena. The film has a first and a second liquid transport direction which are opposite to each other. The first liquid transport direction is from the outer layer towards the absorbent core. Liquid transport in the first direction is larger than liquid transport in the second direction when measured under an identical pressure drop across the apertured film.
This directional liquid transport phenomena is preferably provided by funnel shaped apertures with the direction from larger funnel opening towards smaller funnel opening being parallel to the first liquid transport direction.